The present invention relates to a lens system for forming an equal or nearly equal magnification image of an object such as one to be photocopied, in particular, a catadioptric lens. Such catadioptric lens is often used as a lens system for photocopying, in which the mirror surface is positioned at the rear portion of the lens components and an image is formed in the front of lens components. For example, a lens system having a simple composition is described in British Pat. No. 983,342. However, a catadioptric lens system for use in photo-copy apparatus requires that the F. No. is about 4.5 and the half angle of view is about 24.degree., so that a lens system having a 3 groups of 4 lens components in front of a plane mirror as shown in FIG. 3 is usually used.
On the other hand, another composition is shown in German Pat. Publication No. 1,797,174, wherein a mangin mirror is positioned behind a positive lens, so that, by this convex mirror, a convergent is given to a light flux from an object with free from the spherical aberration.
Further, as described in U.S. Pat. No. 2,742,817, a uni-magnification lens in which a convex mirror of a smaller radius arranged behind of two biconvex lenses and plano-concave lens may be used.